1. Field of the Invention
The present invention is directed to a method of operating a fuel cell vehicle and storing purged hydrogen in a hydrogen trap. More specifically, the present invention relates to a method of operating a fuel cell vehicle where purged hydrogen is stored to a hydrogen trap at park or slow speed conditions and vented at higher speeds.
2. Discussion of Prior Art
Fuel cells have been identified as a potential energy source for vehicles. Fuel cells operate by converting hydrogen and oxygen into electricity. The hydrogen may come from a stored hydrogen container or may be produced on board the vehicle through a reformer.
Hydrogen is always applied under pressure to the anode side of the fuel cell and is consumed as needed to meet the electrical load placed on the fuel cell. Over time, inert gases (nitrogen, argon, etc.) and water accumulate in the anode passageways to an extent that causes fuel cell performance degradation. Periodic purging of these inert gases and water restores fuel cell performance and is accomplished by venting the anode side to force out the inert gases and water. As a result, some hydrogen is also expelled in the purge cycle.
If the fuel cell anode is not periodically purged of inert gases and water, the efficiency of the fuel cell is greatly reduced. The purged hydrogen is normally expelled either through forcing hydrogen through the anode or by removing the hydrogen through the electrolyte. U.S. Pat. No. 5,156,925, (""925) issued Oct. 20, 1992, teaches a method of purging hydrogen from a fuel cell through liquid electrolyte. The electrolyte dissolves the hydrogen gas and carries the hydrogen gas to an electrolyte storage tank. The electrolyte storage tank receives air. The air causes the hydrogen to de-gas from the electrolyte and become vented to atmosphere. A filter prevents the electrolyte from being carried with the purged hydrogen. The ""925 patent does not control the de-gassing or venting of hydrogen. Hydrogen may escape freely from the electrolyte storage container and become vented to atmosphere. This may result in hydrogen being vented from the fuel cell while the vehicle is in a closed environment.
Other patents have also dealt with purged hydrogen gas of a fuel cell. U.S. Pat. No. 5,429,885, (""885) issued Jul. 4, 1995, teaches a method of combining the purged hydrogen gas with oxygen to form water. The invention was intended for use in an underwater vehicle where the hydrogen gas cannot be vented to atmosphere. The ""885 patent teaches the use of a catalytic recombiner to combine the hydrogen and oxygen so that the excess hydrogen does not become vented into the vehicle.
U.S. Pat. No. 5,763,113, (""113) issued Jun. 9, 1998, teaches a method of monitoring the operation of a fuel cell to control the venting of purged hydrogen. The ""113 patent describes how a build-up of hydrogen, water, and inert gases reduces the efficiency of the fuel cell. The gases and water must be periodically removed to maintain the optimum efficiency of the fuel cell. The hydrogen, other gases and water are periodically purged from the fuel cell using a controller that monitors the operating parameters of the fuel cell stack and compares them to known values. As the efficiency of the fuel cell decreases, the hydrogen, other gases, and water are purged from the system. The ""113 patent does not contemplate the unwanted build-up of hydrogen that results from the purging process described. The conditions that lead to a build-up of hydrogen may occur when the vehicle containing the fuel cell is in an enclosed environment.
The present invention anticipates a problem not foreseen in the references described above. The present invention anticipates the venting of hydrogen gas while a vehicle is in an enclosed space. To maintain the efficiency of the fuel cell, the hydrogen is removed from the anode passage, but not immediately vented to atmosphere.
These and other problems of the related art are overcome by the present invention.
The present invention is directed to a method of operating a fuel cell having an anode passage. The method includes collecting hydrogen from the anode passage that does not pass through the catalyst membrane. The hydrogen, together with water and inert gases, are directed to a hydrogen storage container. The hydrogen storage container includes a hydrogen storage media such as metal hydride, carbon adsorbents, or carbon nanofibers.
A sensor determines whether or not the vehicle is moving. When the vehicle is stopped or moving slowly, the surplus hydrogen is directed to the hydrogen storage container for temporary storage. When the sensor determines that the vehicle is moving at a high speed, the surplus hydrogen is vented to atmosphere and the hydrogen storage media is renewed.
Electrically controlled valves direct the purged hydrogen and renew the hydrogen storage media. The valves are controlled by an electronic controller that monitors vehicle speed and hydrogen build-up within the storage media.
These and other desired objects of the present invention will become more apparent in the course of the following detailed description and the appended claims. The invention may best be understood with reference to the accompanying drawings, wherein illustrative embodiments are shown.